//leetcode 37 解数独
public class Test2 {
    boolean[][] row, col;
    boolean[][][] grid;
    public void solveSudoku(char[][] board) {
        row = new boolean[9][10];
        col = new boolean[9][10];
        grid = new boolean[3][3][10];
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (board[i][j] != '.') {
                    int num = board[i][j] - '0';
                    row[i][num] = col[j][num] = grid[i/3][j/3][num] = true;
                }
            }
        }
        dfs(board);
    }

    private boolean dfs(char[][] board) {
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (board[i][j] == '.') {
                    for (int num = 1; num <= 9; num++) {
                        if (!row[i][num] && !col[j][num] && !grid[i/3][j/3][num]) {
                            board[i][j] = (char)('0' + num);
                            row[i][num] = col[j][num] = grid[i/3][j/3][num] = true;
                            if (dfs(board)) return true;
                            board[i][j] = '.';
                            row[i][num] = col[j][num] = grid[i/3][j/3][num] = false;
                        }
                    }
                    return false;
                }
            }
        }
        return true;
    }
}
